1. Field of the Invention
The present invention relates to the use of coherent energy pulses, as from high power pulsed lasers, in the shock processing of solid materials, and, more particularly, to the process of improving properties of such solid materials by providing shock waves therein by tailored multiple laser beam impacts to the solid material. The invention is especially useful for enhancing or creating desired physical properties such as hardness, strength, and fatigue strength.
2. Description of the Related Art
Known methods for the shock processing of solid materials, particularly known methods for the laser shock processing of solid materials, typically use coherent energy from a laser beam oriented normal to a workpiece.
Typical laser shock processing techniques and equipment can be found in U.S. Pat. No. 5,131,957 to Epstein.
Particular types of workpieces used with shock peening include such items as gas turbine engine blades, integrally bladed rotors, a.k.a Blisks, disks, turbine components, and other metallic or alloy materials. Some of these items need laser shock processing on opposite sides of the workpiece. In this type of situation, a process known as split beam processing is used in which a single laser beam is generated and split through various optics to generate two laser beams that impact opposite sides of the workpiece at approximately the same time.
It has been found that on some of these relatively thin sections, such as the blades of gas turbine engines, or other types of turbine blades, the use of relatively long duration, high-energy pulses used to create residual compressive stresses therein, do not create the residual compressive stresses to the level that would normally be expected in a typically thick specimen. With such relatively thin pieces, the shock wave from one side reflects from the other side with sufficient amplitude to alter the distribution of compressive residual stresses on the other side.
What is needed in the art is a method to eliminate or minimize such interaction problems with a relatively thin workpiece sections, and possibly also relatively thick sections.